In the Mac version of SketchUp, none of the tooltips in Tool Palettes for extensions work in horizontal configuration, even with the extensions that come with SketchUp such as Advanced Camera Tools and Sandbox tools. Large Tool Set and Solid Tools are exceptions to this as they have two columns of icons and don't flip betwen horizontal and vertical so the tooltips always work in those two.
The tooltips can work in vertical orientation, but only if you change to vertical then restart SketchUp. If you leave all your tool palettes vertical, the tooltips will work even after closing them and opening them in different SketchUp sessions. This is not a great workaround though as I'd prefer the long ones to be horizontal as my screen width is bigger than its height.
To switch to horizontal, drag the tool palette to the top of the screen. To switch to vertical, drag it to the left of the screen.
